Various types of electrodes are used for electrical contact or electrical measurement in electrical outlets, plugs, or switchboards. If an exposed electrode causes a current leakage, an electric shock may occur. The human body may get an electric shock when an electric current, of which level is higher than a specific value, flows from a power source to the ground surface through the human body. In general, a current that is greater than 15 mA causes human bodies to convulse, and a current greater than 50 mA may kill humans. The main cause of death is heart attack, in which an electric current flowing through the heart damages nerves and causes the heart to stop working. The risk of electric shock depends on the body resistance when an electric current is passed to the human body, and the body resistance varies depending on the condition of the skin.
When electric equipment, such as an electrical outlet, an electric heater, or an electric lamp, is submerged in water, and a human body contacts water or a metal housing to which an electric current is applied through water, the electric current flows from an exposed conductor of electric equipment to the ground surface through water and the human body. In this case, the wet skin, which has a very low contact resistance, leads to the risk of electrocution.
Korea Patent Publication No. 10-2005-0037986 published on Apr. 25, 2005 discloses an electric shock prevention apparatus for preventing electric shock resulting from water immersion, in which in cases of water immersion, electric current leakage from an exposed charging part may be conducted to a conductive metal plate or a conductive metal net which is attached to the exposed charging part, such that an electric shock may be prevented. The metal plate or metal net is connected through wires to a neutral line or an earth terminal among terminal stands, and the size of the metal plate is about 50 cm×30 cm.
While its principle is not described in detail, it appears that in cases of water immersion, an electric current may be prevented from flowing into the human body by interposing a metal plate between submerged conductors having a resistance much lower than the resistance of water and the human body so that the metal plate may be electrically arranged in parallel with the human body. However, the metal plate or the metal net is connected to a terminal stand through a separate wire, and has a huge volume, and thus the space for installation is limited.
Korean Patent No. 10-1197414 published on Nov. 5, 2012 discloses another apparatus for preventing a current leakage, which includes: a connection terminal stand which includes a first connection terminal and a second connection terminal that are disposed between an input terminal and an output terminal and are connected to a phase voltage terminal and a neutral point terminal; and a current leakage preventing conductor that is electrically connected to the second connection terminal connected to the neutral point terminal, so as to surround a lateral side and a top side of the connection terminal stand.
The apparatus for preventing a current leakage has a complicated structure including an electrode that surrounds a connection terminal stand and is connected to a neutral point terminal. Further, it is difficult to apply the apparatus to a small electrical outlet and the like.